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KS4 Chemistry. Halogens. Contents. Halogens. Electron structure and reactivity. Physical properties. Reactions. Uses. Summary activities. 7. He. Li. Ne. Na. Ar. K. Kr. Xe. Rb. Cs. Fr. Rn. Sg. Cd. Hf. Ra. Ac. Rf. Db. Bh. ?. Mt. Ds. Rg. ?. ?. Ta. ?. ?. Hs.

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KS4 Chemistry

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Ks4 chemistry

KS4 Chemistry

Halogens


Contents

Contents

Halogens

Electron structure and reactivity

Physical properties

Reactions

Uses

Summary activities


Group 7 the halogens

7

He

Li

Ne

Na

Ar

K

Kr

Xe

Rb

Cs

Fr

Rn

Sg

Cd

Hf

Ra

Ac

Rf

Db

Bh

?

Mt

Ds

Rg

?

?

Ta

?

?

Hs

Re

Y

Ru

H

Po

Os

Ir

Pt

Au

Hg

Tl

Rh

Pb

Sr

At

W

?

Zr

Nb

Mo

Tc

Bi

?

Al

La

Se

Mn

Te

I

Ca

Sc

As

V

S

Cr

Fe

Co

Ni

Cu

Zn

Ga

Ge

Sb

Ti

Ba

Mg

Cl

Ag

Pd

In

C

Si

P

Sn

F

Cl

B

N

Br

O

F

At

I

Br

Be

Group 7 – the halogens

Halogens are in group 7 of the periodic table, on the right.


Electron structure

Electron structure

All halogens have 7 electrons in their outer shell.

This means that:

fluorine

2,7

  • They can easily obtain a full outer shell by gaining 1 electron.

chlorine

2,8,7

  • They all gain an electron in reactions to form negative ions with a -1 charge.

  • They have similar chemical properties.

bromine

2,8,8,7


Electron structure and reactivity

F

Cl

Br

decrease in reactivity

I

Electron structure and reactivity

All halogens are reactive, and the reactivity decreases down the group. What is the reason for this?

  • The size of each element’s atoms, and the number of full electron shells, increases down the group.

  • This means that, down the group, the outer shell gets further away from the nucleus and is shielded by more electron shells.

  • The further the outer shell is from the positive attraction of the nucleus, the harder it is to attract another electron.

  • This means that reactivity decreases with the size of the atom.


Halogen molecules

F

F

F

F

Halogen molecules

All halogen atoms require one more electron to obtain a full outer shell and become stable.

Each atom can achieve this by sharing one electron with another atom to form a single covalent bond.

+

This means that all halogens exist as diatomicmolecules:F2, Cl2, Br2 and I2.


Contents1

Contents

Contents

Halogens

Electron structure and reactivity

Physical properties

Reactions

Uses

Summary activities


General properties

fluorine is pale yellow

chlorine is green-yellow

bromine is red-brown

iodine is blue-black

General properties

All halogens are:

  • non-metals and so do not conduct electricity;

  • brittle and crumbly when solid;

  • poisonous and smelly.

They become darker in colour down the group:


Physical state of halogens

Halogen

Melting point (°C)

Boiling point (°C)

State

Relative size

Physical state of halogens

The melting and boiling points of halogens increase down the group, as the molecules become bigger.

-220

-118

gas

fluorine

-101

-34

gas

chlorine

-7

59

liquid

bromine

114

184

solid

iodine

What is the state of each halogen at room temperature?


Melting and boiling points of halogens

Melting and boiling points of halogens


Halogen vapours

When iodine is heated gently, it changes directly from a solid to a gas without first becoming a liquid.

This is called sublimation.

Halogen vapours

Bromine and iodine are not gaseous, but have low boiling points. This means that they produce vapour at relatively low temperature. They are volatile.

Bromine produces a red-brown vapour.


True or false

True or false?


Contents2

Contents

Contents

Halogens

Electron structure and reactivity

Physical properties

Reactions

Uses

Summary activities


Reactivity of halogens

Halogen

Reactivity with hydrogen

decrease in reactivity

Astatine is the halogen that appears directly below iodine in the periodic table. How do you think astatine would react with

hydrogen?

Reactivity of halogens

The reactivity of halogens decreases down the group. This can be demonstrated by comparing how they react with hydrogen.

Reacts instantly, even at -200°C.

fluorine

Reacts slowly in the dark. Explodes in the light.

chlorine

Needs heating to +200°C in order to react.

bromine

Does not react completely, even at 500°C.

iodine


Halides

Halogen

Halide

(F )

(Cl

)

-

-

fluorine

(F)

fluoride

(Cl)

chlorine

chloride

(Br

)

(I

)

bromine

bromide

(Br)

-

-

iodine

iodide

(I)

Halides

When halogens react with another substance, they become ions. When this happens, they are called halides.

The name of the halogens change slightly once they have reacted – instead of ending with ‘–ine’, they end with ‘-ide’.

reaction


Displacement reactions

sodiumchloride

sodiumfluoride

+

+

fluorine

chlorine

+

+

F2(aq)

2NaCl(aq)

2NaF(aq)

Cl2(aq)

Displacement reactions

If a halogen is added to a solution of a compound containing a less reactive halogen, it will react with the compound and form a new one. This is called displacement.

A more reactive halogen will alwaysdisplace a less reactive halide from its compounds in solution.


Displacement of halogens

Displacement of halogens

Why will a halogen always displace a less reactive halogen?


Displacement theory

-

+

Na

Cl

-

Cl

F

fluoride

Displacement theory

If a metal halide is mixed with a more reactive halogen,the extra electron will be transferred from the less reactive to the more reactive halogen.

sodium

chloride

chlorine

fluorine


Displacement reactions of halogens

Displacement reactions of halogens


Displacement reactions summary

salt (aq)

potassiumchloride

potassiumbromide

potassiumiodide

halogen

chlorine

bromine

iodine

Displacement reactions: summary

The reactions between solutions of halogens and metal halides (salts) can be summarised in a table:

X

2KCl + Br2

2KCl + I2

X

no reaction

2KBr + I2

X

no reaction

no reaction


Is there a displacement reaction

Is there a displacement reaction?


Reactions of halogens with metals

iron (III)chloride

+

chlorine

iron

+

3Cl2(g)

2Fe(s)

2FeCl3(s)

Reactions of halogens with metals

The reactivity of halogens means that they readily react with most metals.

Halogens need to gain electrons for a full electron shell and metals need to lose electrons for a full electron shell.

This means that halogens and metals react to form ionic compounds. These are metal halides, which are a type of salt.

Chlorine reacts vigorously with iron after gentle heating, despite iron’s low reactivity.


More reactions of halogens with metals

iron (III)iodide

iron (III)bromide

+

+

bromine

iodine

iron

iron

+

+

3Br2(g)

3I2(g)

2Fe(s)

2Fe(s)

2BrCl3(s)

2ICl3(s)

More reactions of halogens with metals

Bromine reacts steadily with iron when heated constantly.

Iodine reacts slowly with iron when heated constantly.


Reactions of halogens with non metals

hydrogen chloride

H

Cl

Cl

H

Reactions of halogens with non-metals

Halogens also react with non-metals.

For example, halogens react with hydrogen to create hydrogen halides.

hydrogen

chlorine

Unlike their reactions with metals, halogens share electrons with non-metals, and so react to form covalent compounds.

All hydrogen halides are gases. They dissolve easily in water and become strong acids.


Reactions of halogens summary

Reactions of halogens: summary


Contents3

Contents

Contents

Contents

Halogens

Electron structure and reactivity

Physical properties

Reactions

Uses

Summary activities


Uses of fluorine

fluorine

and its

compounds

Uses of fluorine

Toothpaste,

to prevent tooth decay

Fluoridation of water, to prevent tooth decay

Polymers,e.g. Teflon fornon-stick pans

Processing uranium nuclear fuel


Uses of chlorine

chlorine

and its

compounds

Uses of chlorine

Antiseptics and disinfectants

Treatment of drinking water

Pesticides and weed killers

Chlorinated carbon compounds, e.g. solvents and plastics (PVC)

Bleach to kill bacteria and to make paper white


Uses of bromine and iodine

Uses of bromine and iodine

bromine

and its

compounds

iodine

and its

compounds

Leaded petrol

Medicines

Photography

Agriculture

Antiseptics and water purification tablets

Animal feed supplements


Contents4

Contents

Halogens

Electron structure and reactivity

Physical properties

Reactions

Uses

Summary activities


Glossary

  • diatomic –An element that exists as molecules containing two atoms covalently bonded.

  • displacement – The reaction when a more reactive halogen reacts with a compound containing a less reactive halogen.

  • halide – The name of a halogen when it has reacted withanother substance and gained a full outer electron shell.

  • halogen – An element that belongs to group 7 of the periodic table.

  • hydrogen halide – A compound formed from the reaction between hydrogen and a halogen.

  • metal halide –A compound formed from the reaction between a metal and a halogen.

  • sublime – To change from a solid to a gas without first becoming a liquid.

  • volatile – A substance that evaporates or produces vapour

at relatively low temperature.

Glossary


Anagrams

Anagrams


Halogens vs halides

Halogens vs. halides


Multiple choice quiz

Multiple-choice quiz


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